Eugene Aserinsky (1921 – 1998) was a graduate student at University of Chicago in 1953 when he discovered REM sleep. He made the discovery after hours spent studying the eyelids of sleeping subjects. His PhD adviser, Nathaniel Kleitman, and Aserinsky went on to demonstrate that this "rapid-eye movement" was correlated with dreaming and a general increase in brain activity. They pioneered procedures that have now been used with thousands of volunteers using the electroencephalograph. Because of these discoveries, Aserinsky and Kleitman are generally considered the founders of modern sleep research.